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The classic for mesuring axial displacement in boreholes

Extensometers are among the most frequently used instruments for measuring the axial deformation along a borehole. They are used for monitoring support and anchoring systems in slope protections, open cuts, underground constructions etc. or to observe settlement and sliding. Several single extensometers can be bundled into multiple extensometers with anchoring points in different depths. This way, it is possible to identify the areas where movement has occurred. The magnitude and progression over time of these movements are valuable indicators for assessing stabilizing measures and help specify the necessary anchor length.

Principle of operation

The anchoring part which is fixed in the rock is firmly connected with measuring rods that transmit movements to a measuring stop in the measuring head, which is anchored to the mouth of the borehole. In this way, the relative movement between the anchor and the mouth of the borehole can be established by sensing the distance between the measurement head and the measuring stop fixed to the measuring rods.

This is performed with a dial gauge or electric displacement tanducers. This measured value can be converted to an elongation value ΔL/L. For protection and for mechanical installation reasons, the measuring rods run inside a pipe between the anchor part and the measuring head. This pipe is designed so that it does not influence the movement of the anchor part and the rods, which would cause erroneous reading. 

Tailor-made variants

Depending on the measuring task and ambient conditions, different versions are possible. For fractured rock, our packer anchor parts can be used to prevent the loss of injection material and ensure a frictional connection with the borehole wall. The measuring heads are designed to be equipped with electrical displacement transducers – even at a later date. Numerous variants with different measuring paths up to pressure watertight models are also available for this purpose. 

The measuring rods usually consist of corrosion-resistant GRP rods with a diameter of 10 mm. In combination with the PVC cladding tube, it is possible to easily adapt the lengths to the conditions immediately before installation on site. If required, galvanised steel or stainless steel can also be supplied.

Our services

We deliver all components in the desired design. Our technicians are also happy to carry out the installation on site. If an automatic measurement data acquisition is desired, we plan and deliver optimized solutions and accompany our customers until commissining.

Highlights

  • Possible installation lengths of up to approx. 130 m
  • Simple extensometers can be combined to up to 6-fold extensometers at no extra expense
  • Numerous variants available for adaptation to installation situation
  • Robust and durable design
  • Simple retrofitting for automatic data acquisition
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